1. Field of the Invention
This invention relates to an optical disc drive for playing back or recording and playing back an optical disc and a method of controlling the optical disc drive.
2. Description of the Prior Art
There are known optical disc drives for playing back (reproducing) or recording and playing back an optical disc such as a CD (compact disc), CD-ROM, CD-R (CD-Recordable) and CD-RW (CD-Rewritable).
In the conventional optical disc drives, when the disc drive is to be operated once after the rotation of the optical disc has been stopped, various servo controls such as a focus servo, a tracking servo and a sled servo must be carried out in the process of accelerating the rotational speed of the optical disc so that its rotation number becomes the same as that of the previous operation. Further, in recent years, the rotation speed (data transmission speed) of the optical disc tends to increase to a multiple times rotation speed (for example, from 2xc3x97 to 4xc3x97, 6xc3x97, 8xc3x97, 12xc3x97, 16xc3x97, 24xc3x97, 32xc3x97 and the like).
Meanwhile, in the commercially available optical discs, there is a case that poor eccentric optical discs (optical discs having unbalanced weight distribution) are included therein. When the rotation speed of such an eccentric optical disc is to be accelerated in order to rotate the optical disc at a high speed, larger vibration is likely to occur as compared with the case where a normal optical disc is rotated at a high speed. When such large vibration of the optical disc drive is transmitted to an optical pick-up, it gives rise to a problem in that various servo controls such as a focusing servo and a tracking servo are not engaged properly.
In view of the problem as described above, the object of the present invention is to provide an optical disc drive which can perform various servo controls properly even when the rotational speed of the optical disc is accelerated to a high rotation speed once after the rotation of the optical disc has been stopped.
In order to achieve the object, the present invention is directed to an optical disc drive for playing back or recording and playing back an optical disc. The disc drive comprises an optical disc driving mechanism for rotating an optical disc; an optical pick-up having an objective lens which is actuated by servo operation; signal processing means for processing signals read out from the optical disc through the optical pick-up; and control means for controlling the optical disc rotating mechanism, the optical pick-up and the signal processing means. The controlling means includes initial control means for controlling the optical pick-up rotating mechanism and the optical pick-up so that, when the rotation number of the optical disc is to be increased to a first target rotation number, the rotation number of the optical disc is provisionally set to a second target rotation number which is smaller than the first target rotation number, and at least the servo operation of the optical pick-up is caused to engage until the rotation number of the optical disc reaches the second target rotation number.
According to the optical disc drive of the present invention as described above, it is possible to provisionally set the rotation number of the optical disc to the second rotation number when the rotation number of the optical disc is increased to the first target rotation number, and the various servo controls such as the focus servo control, the tracking servo control and the sled control can be performed until the rotation number of the optical disc reaches the second target rotation number.
Therefore, it becomes possible to perform the focus servo, the tracking servo and the sled servo properly and reliably even if an eccentric (unblanced) optical disc is used.
In this invention, it is preferred that the initial control means is operated when the rotation number of the optical disc is to be increased to the first target rotation number from the state that the optical disc drive is turned on. Alternatively, it is also preferred that the initial control means is operated when the rotation number of the optical disc is to be increased to the first target rotation number by re-starting the rotation of the optical disc once after the rotation of the optical disc has been stopped.
Further, in the present invention, it is preferred that the initial control means is operated only when the fist target rotation number exceeds a predetermined reference rotation number.
Further, it is also preferred that the mean acceleration of the optical disc from the second target rotation number to the first target rotation number is larger than the mean acceleration of the optical disc from the start of the optical pick-up rotating mechanism to the second target rotation number.
Furthermore, the servo operation of the optical pick-up to be controlled includes at least one of a focus servo and a tracking servo.
It is preferred that the optical disc drive of the present invention further comprises means for automatically adjusting a predetermined signal used in the optical disc drive, wherein the adjustment of the predetermined signal is adapted to be performed until the rotation number of the optical disc reaches the second target rotation number. In this case, the adjustment of the predetermined signal includes at least one of adjustment of amplitude of the signal read out from the optical disc and adjustment of a reference level for canceling offset components in the signal.
The other aspect of the present invention is directed to a method for controlling an optical disc drive for playing back or recording and playing back an optical disc. The method comprises the steps of: starting rotation of an optical disc so that the rotation number of the optical disc becomes a first target rotation number; increasing the rotation number of the optical disc provisionally to a second target rotation number which is smaller than the first target rotation number; causing servo control of an optical pick-up to engage until the rotation number of the optical disc reaches the second rotation number; and increasing the rotation number of the optical disc from the second target rotation number to the first target rotation number.
In this method, it is preferred that the method is carried out when the optical disc is started to rotate from the state that the optical disc drive is turned on.
Further, it is also preferred that the method is carried out when the optical disc is re-started to rotate once after the rotation of the optical disc has been stopped.
It is also preferred that the method further comprises the step of determining whether or not the fist target rotation number exceeds a predetermined reference rotation number, and only when the fist target rotation number exceeds the predetermined reference rotation number, the rotation number of the optical disc is provisionally increased to the second target rotation number.
Further, it is also preferred that the mean acceleration of the optical disc from the second target rotation number to the first target rotation number is larger than the mean acceleration of the optical disc from the start of the optical pick-up rotating mechanism to the second target rotation number.
Furthermore, it is preferred that the servo control includes at least one of a focus servo control and a tracking servo control.
Moreover, it is also preferred that the method further comprises the step of performing adjustment of a predetermined signal used in the optical disc drive until the rotation number of the optical disc reaches the second target rotation number. In this case, it is preferred that the adjustment of the predetermined signal includes at least one of adjustment of amplitude of the signal read out from the optical disc and adjustment of a reference level for canceling offset components in the signal.
Other objects, structures and advantages of the present invention will be apparent when the following description of the preferred embodiment is considered taken in conjunction with the accompanying drawings.